1. Field of the Invention
Various embodiments of the present invention relate to wireless network management. One specific example relates to efficient radio frequency (RF) spectrum management involving multiple mobile vehicles.
Other examples of the present invention provide systems and methods to analyze the RF emissions resulting from the motion of transmitters and/or receivers through airspace with the help of five-dimensional quanta of space (x, y, z), time and frequency to assign frequency bands to test plans (including previously-validated test plan(s) and/or to-be-validated test plan(s)). In one specific example, the analysis is directed to the assignment of frequency bands with and without reuse.
2. Description of Related Art
The Department of Defense (“DoD”) runs a number of “test ranges” across the country. These are air fields or the like at which vehicles (typically new models), such as aircraft and/or ground vehicles, are tested while in motion. Telemetry data is typically continuously streamed from the vehicles to “ground stations” over wireless communication channels during the course of a test.
The wireless spectrum required to support the telemetry communication channels in the airspace over the test ranges is a resource for which there is a great deal of contention. For example: bandwidth needs for each test are typically expanding; the number of tests per day to be scheduled at a given test range is typically increasing; and/or the popularity of smart cellular phones has caused contention by commercial entities for the spectrum bands that were previously designated for telemetry.
In one conventional technique, spectrum de-confliction is approached with spatial allocations of the right to transmit, and with gross approximations. This approach attempts to compensate for the inherent difficulty of making fine-grained spectrum assignments simultaneously in the space, time and frequency domains. However, the result of this approach is that huge amounts of spectrum are typically wasted.
For example, at the most approximate level, a user (typically an enterprise) could be awarded “use of the upper L Band, from 1735-1855 MHz”. This implies that the time dimension is approximated to perpetuity. There could be long periods when the user does not transmit at all, when the spectrum could potentially be put to better use. The space dimension too is typically approximated to all space being controlled. There would be many parts of space where no one is transmitting at that frequency at many different times—and where the same spectrum could potentially be put to better use.
In another conventional technique, a frequency manager at a test range manually plans spectrum for an upcoming test by designating a “flight area”—a volume of airspace surrounding the flight path of a test article—and maintaining a reservations calendar for it (giving the frequency manager a right to transmit at certain frequencies in pre-allocated blocks of space for pre-designated blocks of time). The calendar is typically posted at a web-site, which can typically be accessed by other frequency managers.
There are a number of down-sides to this technique.
One downside is that the space allocation is approximated to a “flight-area” surrounding a test range. This is an unnecessarily large space. A transmitter, assigned a certain frequency, may in reality be only transmitting in one part of the airspace. The spectrum in the rest of the space is thus typically wasted.
Another downside is that the space allocation also presents problems at the boundaries. If a transmitter is close to a boundary, although it is emitting from within the flight area, the emission could leak into an adjacent space where it could cause interference. This then necessitates a “guard space” surrounding the space allocation, which leads to further wastage of potential spectrum (already, there is concern that frequency de-confliction needs to occur between test ranges that are close to each other).
Another downside is that the technique typically precludes frequency reuse. There may be multiple opportunities for transmitters to transmit at the same frequency in different parts of the airspace without interfering with one another. This is especially true when directional antennas are employed. These opportunities for frequency reuse are typically wasted with this technique.
Another downside is that the time allocation is a gross approximation, typically 24 hours allocated to a test. This compensates for the uncertainty surrounding the take-off times of flights within the test plan. However, if an aircraft is going to be in the air for only part of the time during a test and it is assigned a certain frequency, that frequency could be used while the aircraft is not in the air.
Another downside is that the gross time allocation also attempts to compensate for the ‘lateness’ of an aircraft. Because it is not guaranteed that an aircraft will take off on time, a large time-buffer is typically allotted in case it takes off late. Since the aircraft's lateness is not bounded in any real sense, potential spectrum is wasted.
Another downside is that the technique does not typically make use of the flight plan information of a test article. A slow-moving aircraft could traverse a long flight corridor. Spectrum is reserved through the entire corridor. But, in reality, once the aircraft finishes traversing a portion of the flight corridor, the spectrum in that part could potentially be used for other purposes.
Finally, another downside is that the technique typically restricts the airspace management scope of the system to certain flight areas. But, in practice, this poses unnecessary constraints. With crowding, airspace boundaries may need to change fluidly to exploit opportunities for testing. New flight corridors may open up for flying tests, while other areas may have to be designated as off-limits, perhaps on a dynamic basis.
As mentioned, because of the complexity of reserving frequency bands for different volumes of airspace over time, and the potential cost of making a mistake, the conventional reservations calendar technique tends not to be very granular. Available frequency bands are typically missed, because of a natural tendency to schedule an important test in isolation, with “nothing else going on”.
Further, there is typically an imprecise characterization of “lateness”, the possibility that a test article may embark on its flight path later than the scheduled time (e.g., due to unforeseen events). As a consequence, the guard time intervals between tests tends to be unduly large, causing a wastage of available spectrum. If the test involves, for example, a slow-moving craft covering a long flight path, the typical tendency is to reserve airspace along the entire flight path, rather than free up for other tests the airspace that has already been traversed.
Another conventional technique implements frequency reuse with spatial allocations. In this technique, the airspace is divided up into blocks. Transmitters in non-adjacent blocks are allowed to transmit at the same frequency. This approach also suffers from the fact that the blocks are gross approximations. The opportunities for transmission or reception with directional antennas within the same block are wasted. Knowledge of flight paths through the blocks is not used. Frequency reuse blocks may necessitate switching frequencies at block boundaries—an added problem.
Further, conventional spectrum planning systems, such as “Spectrum Management Tools” by Sentel Corporation, are available.
Of note, the idea of making hypothetical frequency assignments to RF devices, then performing a worst-case analysis of the resulting emissions has heretofore been considered too complex and too imbued with uncertainty to attempt.